The location of cellular towers, or base-stations, can be used in determining a mobile devices location. A mobile device may receive or detect signals from multiple cell towers at a time, although the mobile device is only in communication with a particular cell tower at a time. The mobile device will camp on a cell tower, that is the mobile device is associated with the particular cell tower, and can communicate using that cellular tower.
FIG. 1 depicts a simplified environment for depicting how cellular tower locations may be used in determining the location of a mobile device. The environment 100 comprises a plurality of cellular towers 102a, 102b, 102c that transmit and receive radio frequency signals. Each cell tower 102a, 102b, 102c has an associated unique identifier depicted as T1, T2, T3 respectively and a location A, B, C respectively. A mobile device 104 may receive radio frequency (RF) signals from one or more of the cellular towers 102a, 102b, and 102c. If the mobile device 104 is able to identify the unique identifiers associated with each of the cellular towers the mobile device sees, the locations associated with the visible towers may be retrieved, for example from a network service, and used to determine an estimate of the location of the mobile device 104. The location of the mobile device 104 is depicted in FIG. 1 as being a simple centroid, or average of the position of the three visible cellular tower 102a, 102b, 102c. Although it is possible to estimate the mobile device's location as a simple centroid, it is possible to estimate the location using different techniques. For example the strength of the signals received from the cellular towers may be used as a weighting value in determining the location estimate. Further, the location of the mobile device may be estimated using fingerprint based techniques that use the radio scene, that is the towers that are visible and their signal strengths, detected at the mobile device and compares it to previously captured radio scenes that are associated with known locations. Regardless of how the location of the mobile device is estimated, it is beneficial if all of the cellular towers that a mobile device sees, that is the cellular towers from which RF signals are detected at the mobile device, can be uniquely identified.
A mobile device only needs to know the unique cellular tower identifier (ID) of the cell tower it is currently camped on. Although it is possible for a mobile device to determine the unique cellular tower identifier of all visible cellular towers, doing so requires additional power consumption, and as such it is typically avoided in mobile devices in order to increase battery life. Although the mobile device does not detect the unique cell tower ID of all visible towers, it does detect non-unique tower parameters of the other visible towers. For example, the non-unique tower parameters may comprise UTRA Absolute Radio Frequency Channel Number (UARFCN) and a Primary Scrambling Code (PSC). Both the UARFCN and the PSC are non-unique parameters that are re-used throughout the network. However, the network architecture typically requires that the UARFCN and PSC of neighboring towers, that is cellular towers that are within the reception area of a mobile device at some location, do not overlap.
Although the unique tower ID of the tower the mobile device is camped on as well as the non-unique tower parameters of the other visible neighboring towers may be used to provide an estimate of the mobile device's location, it would be desirable to be able to uniquely identify the visible neighboring cell towers for use in determining the mobile device's location without requiring the mobile device to expend additional power.